Oh crap. did not realize that people outside my institutions system would not get to the actual paper. Will post some key excerpts.

"Our findings are consistent with work revealing that Whites' racial
prejudice is now typically expressed in a subtle, rationalizable manner (Dovidio & Gaertner, 2004). Whereas the aversive racism framework originally proposed that subtle, indirect manifestations of bias would mainly characterize the responses of low prejudice scoring Whites, while high-prejudice scoring Whites would express their bias more directly (Gaertner & Dovidio, 1986), the increasing strength of egalitarian norms (Schuman et al., 1997)may lead even high-prejudice scoring Whites to express their bias more subtly (Pearson et al., 2009). That is, due to social norms declaring that racial prejudice is inappropriate, even highly prejudiced Whites may feel a need to legitimatize their beliefs about Obama by attributing them to some factor unrelated to race, such as his un-American social policies. Our data support this perspective. Perceptions of Obama's un-Americanism mediated the overall relationship between racial prejudice and negative performance evaluations. However, as anticipated, this effect occurred only for White participants' evaluations of Obama, but not of Biden."

That is, Obama and Biden support the same policies, but only Obama suffers demands to prove that he is American. And what is the obvious difference between these two 50-year old Democratic politicians?